Silver halide light-sensitive materials should be handled in full darkness or under safelight having a wavelength region to which the light-sensitive materials are substantially insensitive. As sensitivity of light-sensitive materials becomes higher, the safelight should have so much reduced quantity of light, which naturally interferes with the ability to easily handle the light-sensitive materials. Therefore, it has been strongly desired to develop a photographic light-sensitive material that can be handled under bright safelight conditions. However, such a light-sensitive material that has high sensitivity but can also be handled under bright safelight has not yet been obtained. In particular, there has been a demand in the field of printing plates that contact exposure using a relatively low sensitive light-sensitive material could be carried out in a bright room. In compliance with this demand, photographic light-sensitive materials which can be handled in an atmosphere that may be called a substantially bright room while using a silver halide as a light-sensitive element have recently been proposed. This proposal can be embodied by a combination of a light-sensitive material having an extremely reduced sensitivity to visible light, i.e., about 1/10.sup.4 to 1/10.sup.5 the sensitivity of conventional photographic light-sensitive materials, and a printor having a powerful light source containing a large quantity of ultraviolet rays. With reference to such a silver halide light-sensitive material that can be handled in a bright room, Japanese Patent Application (OPI) Nos. 125734/81, 149030/81 and 149031/81, etc. (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") disclose silver halide emulsions which are prepared in the presence of a large amount of a rhodium salt. However, these known emulsions exhibit such low sensitivities that they require a long time for exposure even with a powerful light source. Therefore, light-sensitive materials which not only have sufficiently high sensitivities, i.e., can be exposed in a short time, but also can be handled under safelight that may be referred to as bright room conditions has not yet been developed.
On the other hand, it is well known that a light-sensitive wavelength region of a silver halide light-sensitive emulsion can be broadened to a longer side by adding a certain kind of cyanine dyes to the emulsion (spectral sensitization). It is also known that this spectral sensitization can be applied not only to a visible wavelength region but also to an infrared wavelength region. Spectral sensitization can be carried out by using sensitizing dyes showing absorption in a visible or infrared region. Examples of these sensitizing dyes are described, e.g., in Mees and James, The Theory of the Photographic Process, 3rd Ed., 198-201, Macmillan (1966).
When these known sensitizing dyes are used for spectral sensitization in a visible region, the wavelength region of applicable safelight is naturally limited to a narrow range. If in using for spectral sensitization in an infrared region, the resulting light-sensitive material thus sensitized to an infrared region exhibits not only sensitivity to an infrared region but also sufficient sensitivity to a visible region. As a result, the infrared-sensitized light-sensitive material cannot be handled except under safelight conditions of very low lightness or in total darkness. For example, a commercially available infrared sensitive light-sensitive material, Sakura Sekigai 750 (produced by Konishiroku Photo Industry Co., Ltd.) is specified to be handled in total darkness. It is also specified that use of safelight should be limited to lighting for several seconds at the end of development. Similarly, Kodak HIE 135-20, trademark for an infrared sensitive light-sensitive material produced by Eastman Kodak Co., is specified to be handled in total darkness.
In the use of the infrared light-sensitive materials, it has been strongly desired that they can be handled under bright safelight unlike the above-described conventional infrared light-sensitive materials, thus greatly improving workability.
However, as described above, it has so far been impossible to handle light-sensitive materials having increased sensitivity by spectral sensitization under safelight that may be referred to as bright light. Accordingly, light-sensitive materials presently must be selected from the alternatives of those which can be handled under bright safelight but require long exposure due to low sensitivity or those which should be handled under dark safelight but require short exposure due to high sensitivity.